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Pass Functions as Arguments

This DataWeave example defines a base function in the header that receives two arguments: a function and an element to apply it on. The base function the applies the received function onto the keys of the received element and also to every one of its child elements recursively. In this case, the function sent sets all keys to lower case.

The example uses the following:

  • A custom function that is applied recursively, ie: it calls itself for each child in the element it receives originally.

  • mapObject to sort through each child of the element.

  • lower from the Strings library to make every Key in the input lower case.

  • is to check if the passed element is of type Object (and therefore has children).

  • if and else to only have the function call itself when a condition is met, and to otherwise end the recursive loop for that branch.

DataWeave Script:
%dw 2.0
import * from dw::core::Strings
output application/xml
fun applyToKeys(element, func) =
    if (element is Object)
        element mapObject (value, key) -> {
        (func(key)) : applyToKeys( value, func)
        }
    else element
---
applyToKeys(payload, (key) -> lower(key))
Input XML Payload:
<CATALOG>
  <CD>
    <TITLE>Empire Burlesque</TITLE>
    <ARTIST>Bob Dylan</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Columbia</COMPANY>
    <PRICE>10.90</PRICE>
    <YEAR>1985</YEAR>
  </CD>
  <CD>
    <TITLE>Hide your heart</TITLE>
    <ARTIST>Bonnie Tyler</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>CBS Records</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1988</YEAR>
  </CD>
</CATALOG>
Output XML:
<?xml version='1.0' encoding='US-ASCII'?>
<catalog>
  <cd>
    <title>Empire Burlesque</title>
    <artist>Bob Dylan</artist>
    <country>USA</country>
    <company>Columbia</company>
    <price>10.90</price>
    <year>1985</year>
  </cd>
  <cd>
    <title>Hide your heart</title>
    <artist>Bonnie Tyler</artist>
    <country>UK</country>
    <company>CBS Records</company>
    <price>9.90</price>
    <year>1988</year>
  </cd>
</catalog>

See Also